There are many critical factors the pilot of an aircraft must consider when determining if the aircraft is safe for take-off. Some of those factors are identifying the proper weight and center of gravity for the aircraft. Hereinafter, aircraft “Center of Gravity” will be referred to as aircraft “CG.”
Aircraft CG is a critical factor in flight operations. If the aircraft CG is too far aft and outside the aircraft's certified CG limits, the aircraft nose can rise uncontrollably during take-off, where the aircraft will become unstable, resulting in a stall and possible crash.
Furthermore, fuel is the most costly item in an airline's annual expenses. Airline profit margins are slim at best, so any and all efforts must be used to reduce fuel consumption. Aircraft CG location affects the amount of fuel the aircraft burns. If an aircraft is loaded with the CG positioned towards the forward limit of the aircraft's CG envelope, the pilot must add rear stabilizer trim for the nose-heavy aircraft. This additional rear stabilizer trim will increase the aerodynamic drag on the aircraft, thus burn more fuel. If an aircraft can be loaded with the aircraft CG positioned near the aft limit of the aircraft CG envelope, the aircraft will require less trim and be more fuel efficient.
In a search of the prior art, there are numerous onboard aircraft weighing systems which measure aircraft weight. The measured aircraft weight is subsequently used to determine aircraft CG. Research of the prior art to identify automatic aircraft weighing systems are well documented and reference may be made to United States patents:    U.S. Pat. No. 3,513,300—Elfenbein U.S. Pat. No. 5,548,517—Nance    U.S. Pat. No. 3,584,503—Senour U.S. Pat. No. 6,128,951—Nance    U.S. Pat. No. 3,701,279—Harris U.S. Pat. No. 6,237,406—Nance    U.S. Pat. No. 5,214,586—Nance U.S. Pat. No. 6,237,407—Nance    U.S. Pat. No. 5,521,827—Lindberg U.S. Pat. No. 7,967,244—Long
The prior art described by these patents explain mechanical apparatus added to a landing gear strut which measure the weight of the aircraft. Typical aircraft used in day-to-day airline operations are commonly supported by a plurality of compressible, telescopic landing gear struts. These landing gear struts contain pressurized hydraulic fluid and nitrogen gas. The weight of the aircraft rests upon and is supported by “pockets” of compressed nitrogen gas, within the landing gear struts. Aircraft weight supported by these pockets of gas is called the “sprung” weight. There is additional aircraft weight which is not identified by changes in landing gear strut pressure. This additional weight is associated with various landing gear components located below the pockets of compressed gas including such items as the wheels, tires, brakes, strut piston, and other lower landing gear components. Aircraft weight associated with these lower landing gear components located below the pockets of compressed gas is called the “unsprung” weight. Unsprung weight remains a relatively constant weight. Aircraft brake wear and tire wear result in a minimal and virtually insignificant amount of weight loss to the unsprung weight. The unsprung weight is typically added to the sprung weight, to identify total aircraft weight.
The methods of prior art aircraft weighing systems, determine the “sprung” weight of the aircraft by measuring the pressure within the landing gear struts and multiplying strut pressure by the load supporting surface area of the strut piston. Among the disadvantages of the prior art onboard aircraft weight measuring systems are that airlines can suffer severe schedule disruptions by using a “measured” aircraft weight value, as opposed to methods of “calculating” aircraft weight based upon FAA approved “assumed” weights, of varying weight items such as airline passengers and baggage, loaded onto the aircraft.
Aircraft load planning is a crucial part of keeping an airline running on schedule. A scheduled aircraft departure will commence its load planning process up to one year prior to the actual flight. Airlines do not offer ticket sales for a flight, more than twelve months prior to the flight. As each ticket for a scheduled flight is purchased, the average passenger and average bag weights are assigned into a computer program, continually updating throughout the year the planned load for that flight. Aircraft have a maximum design take-off weight limitation, where airline operations use assumptions as to the weight of passengers and baggage loaded onto the aircraft, to stay below the aircraft take-off weight limitation. The Federal Aviation Administration has published an Advisory Circular “AC 120-27E” which designates the approved weight assumptions for airline passengers and baggage:
Average passenger weight - summer190.0 lbsAverage passenger weight - winter195.0 lbsAverage bag weight 28.9 lbsAverage heavy bag weight 58.7 lbs
Historical weather patterns regarding wind velocity and direction, along with storm patterns along scheduled airline routes are also considered when planning the amount of fuel that will be consumed for a potential flight. On the actual day of a flight, typically two hours prior to the departure of that flight, the airline's automated load planning program will be transferred to the desktop computer display of one of the airline's Flight Dispatchers. It is the responsibility of the Flight Dispatcher to then monitor the planned load of that flight as passengers check-in at the gate. Typically this process goes without interruption and the aircraft will dispatch on schedule, as planned. As the door of the aircraft is closed and the load is closed-out by the Flight Dispatcher, the planned load will always match the departure load, as submitted to the FAA, because both are based on the same compilation of weight assumptions. If there were a system onboard the aircraft that measures the aircraft weight, just as the aircraft door closes, and the measured weight did not match the calculated weight, the airline would be forced to take a departure delay to resolve the differential in the two separate but parallel weight determination processes. This potential for delay in the flight departure, on as many as 2,200 daily flights for a single airline, results in the various airlines not willing to take the risk of hundreds of flight delays. Airlines currently dispatch their aircraft under FAA approved procedures; a method which helps keep the airlines on schedule. This creates an incentive for airlines to continue to use the FAA approved assumed weights, irregardless to whether the assumed aircraft weight determination is accurate.
Airlines would appreciate an opportunity to use the CG tracking capabilities of today's aircraft weight and balance systems to more efficiently place baggage and cargo below decks, and take advantage of the reduced fuel consumption benefits, but are not willing to take the risk of scheduled departure delays when the aircraft's planned weight, built upon weight assumptions, does not match the aircraft's actual measured weight.
The methods described herein are applicable as alternatives to existing prior art aircraft weight and balance measuring systems for determining aircraft CG, independent of measuring the aircraft weight.